TLDThe Model 4488 Dry Air Generator is an automatic, standalone unit which produces clean, dry air suitable for use in any Harshaw TLD hot gas reader, including Models 4500, 5500, 6600, and 8800.
Product Detail
This unique dry air generator allows users the maximum control with minimum maintenance. The Harshaw 4488 is electronically driven with two alternately operating desiccant-type dryers.
As atmospheric air is drawn into the unit, it is first filtered, then compressed and passed through the cooler and the dryer. At that point the humidity is measured and, if it is excessive, the air is dumped to the atmosphere. If the humidity is acceptable, the air passes into the reserve storage tanks. From there it is released to the TLD reader at a regulated pressure of 4.14 bar (60 psi), based on the setting of the output regulator.
The compressor is an electrically driven, two piston unit with a capacity of 28.3 l/s (60 cubic feet per hour). The primary filters are located in the air intake, with a particle size of 10 microns.
The two desiccant-type dryers operate alternately; as one is drying the compressed air, the other is being purged of moisture by low pressure air flow. The flow cycles from one dryer to the other every thirty seconds. If one dryer saturated before thirty seconds of use, the humidity alarm is activated and the air is dumped to the atmosphere. When the air flow cycles to the other dryer and is dry, the flow is directed to the reserve tanks and the alarm stops.
The compressed air is maintained in two 0.98 l (60 cu. in.) tanks connected in series. When the tank pressure drops below 4.42 bar (65 psi), the compressor re-starts and runs until the pressure reaches 5.44 bar (80 psi), at which point it stops.
The unit is started by pushing the "ON/OFF" switch into the ON position. The red "POWER" light will come on. If the unit had been sitting idle for any length of time, the "RELATIVE HUMIDITY HIGH" light will also come on, as will the audible alarm. The "AUDIBLE ALARM" switch may be turned off, but the light will stay on until the desiccant chambers are purged of all moisture. When the "RESERVE" pressure reaches 5.44 bar (80 psi), the compressor will shut off and the system is ready for use. When the system is turned off, the reserve air is vented to the atmosphere.
Controls
All the controls and adjustments necessary for the operation of the system are grouped in the front control panel of the 4488 Dry Air Generator. These controls are briefly described as follows:
ON/OFF RESET - This two position switch is used to turn power on and off. It is also the reset button for the circuit breaker.
POWER- This is an indicator light that shows when the power is turned on.
RESERVE PRESSURE - This gauge shows the pressure in the reserve tanks. It should run between 65 and 80 psi. This pressure is set automatically: there are no user adjustments to control this pressure.
OUTPUT PRESSURE - This gauge shows regulated pressure available for the TLD Reader. The normal reading for this gauge is 60 psi.
OUTPUT REGULATOR - this knob adjusts the pressure regulator which controls the pressure of the air to the TLD Reader. It should be adjusted to show 60 psi on the OUTPUT PRESSURE gauge.
Maintenance
The only recommended preventive maintenance is to change the filters and the desiccant units once per year under normal operating conditions. These parts are available from us.
Humidity Monitor
This area of the Control Panel contains functions related to monitoring the humidity of the compressed air. Note that there are no adjustments for humidity, only warnings.
POWER - This indicator light shows that power is turned on for the humidity sensor circuit.
3%, 6%, 9% - These indicator lights come on to indicate the humidity level of the compressed air. When at first starting the unit, they may all come on and turn off successively as the air is dried.
RELATIVE HUMIDITY HIGH - This red light is an alarm warning; it is activated when the humidity is greater than 3%.
AUDIBLE ALARM - This is the speaker for the high humidity alarm; it is activated when the humidity is greater than 3%.
AUDIBLE ALARM ON/OFF - This switch turns the audible alarm on or off. This switch should be left in the on position at all times, until an alarm sounds. It may then be turned off until the air is dry, then is should be turned on again.
PUSH TO TEST - this button is used to test the humidity monitoring system. Pressing this button will check the circuit and light the 3%, 6%, and RELATIVE HUMIDITY HIGH indicator lights in succession and sound the audible warning.
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